1. Field of the Invention
The present invention relates generally to electrochemical measuring apparatus and, more particularly, to apparatus for measuring ionic species in solution. The apparatus is particularly advantageous for measuring a substance reactable with an electrolyte by monitoring a change in ion concentration of the electrolyte when reacted with the substance.
2. Description of the Prior Art
U.S. Pat. No. 4,003,705, assigned to the assignee of the present invention, describes an electrochemical analysis apparatus for measuring carbon dioxide in serum employing a common solution ground and a pair of electrolyte flow-through pH sensors having respective electrolyte chambers connected in series for flowing fresh electrolyte to each chamber prior to sample measurement. The serum sample is reacted with an acid reagent in a sample chamber to release carbon dioxide which diffuses through a gas-permeable membrane into the electrolyte space of one of the pH sensors to react with the electrolyte therein. Upon reacting with the carbon dioxide, the electrolyte undergoes a change in pH. By contrast, the second pH sensor and solution ground is located in the series electrolyte flow path remote from the first sensor and is not exposed to the carbon dioxide. The outputs of the respective pH sensors are connected to first and second high impedance inputs of a differential amplifier to derive a differential pH signal at the amplifier output. The differential pH signal, in turn, is differentiated to provide an output signal the maximum value of which provides a measure of the carbon dioxide content in the sample.
While the foregoing apparatus represents an advance in the art of electrochemical analysis, it does so with a moderate degree of electronic and mechanical hardware. That is, a pair of pH sensors, each comprising a standard glass pH measuring electrode, are utilized to develop the differential pH signal, and the noted differential amplifier is employed for processing the signal. Accordingly, it would be desirable to achieve the foregoing electrochemical measurements with an arrangement of reduced electronic and mechanical complexity.